A planet four times the size of Earth may be skirting the edges of the solar system beyond Pluto, according to new research. Too distant to be easily spotted by Earth-based telescopes, the unseen planet could be gravitationally tugging on small icy objects past Neptune, helping explain the mystery of those objects' peculiar orbits.

The claim comes from Rodney Gomes, a noted astronomer at the National Observatory of Brazil in Rio de Janeiro. Gomes presented his recently completed computer models suggesting the existence of the distant planet at a meeting of the American Astronomical Society in Timberline Lodge, Ore., earlier this month.

Astronomers who attended the talk find Gomes' arguments compelling, but they say much more evidence is needed before the hypothetical planet can be crowned as real.

For several years, astronomers have observed that a handful of the small icy bodies that lie in the so-called "scattered disc" beyond the orbit of the planet Neptune, including the dwarf planet Sedna, deviate from the paths around the sun that would be expected based on the gravitational pulls of all the known objects in the solar system.

Sedna, for example, swings around the sun in an extremely elongated orbit — tracing out a very long oval. "Sedna's orbit is truly peculiar," said Mike Brown, an astronomer at Caltech who led the team that discovered Sedna in 2003.

However, when Gomes ran the same calculations with the addition of the gravitational pull of a massive planet at the outskirts of the solar system, Sedna and the other anomalous objects' expected orbits fell in line with observations. The unseen planet would be too far away to perceptibly perturb the motions of Earth and the other inner planets, but close enough to the scattered disc objects to sway them. [The True Stories of 5 Mystery Planets]

Unknown entity

Several planet types could fit the disturbances seen in Gomes' calculations. For example, a Neptune-size planet, about four times bigger than Earth, orbiting 140 billion miles (225 billion kilometers) away from the sun would influence the anomalous objects in the observed manner. Or, a Mars-size planet with a highly elongated orbit — but one that always kept it well beyond the orbit of Pluto — could yield similar results. As for how it got there, the planet could have been born in and expelled from a distant star system and later captured by our sun's gravity, Gomes said, or it could have formed near our sun and gradually been thrust outward through gravitational interactions with the other planets.

Though Gomes' work has not yet been peer-reviewed, his colleagues are confident he got the math right. "[Gomes] is very good. It's hard to imagine he made a mistake in his calculations," said Hal Levison, a planetary scientist at the Southwest Research Institute in Boulder, Colo.

"Rodney Gomes is actively seeking further evidence and I await his findings with interest!" Douglas Hamilton, an astronomer at the University of Maryland, told Life's Little Mysteries. "He has taken on a difficult task, but is taking the right approach. It is definitely a high risk, high reward, situation — a discovery of a new planet would be spectacular!"

New planet or old star?

This would not be the first time a planet was revealed by way of its gravitational effects on other celestial bodies. The existence of Neptune was hypothesized at the turn of the 19th century — long before the gas giant was actually seen through a telescope in 1846 — because of the way it was perturbing the orbit of Uranus.

On the other hand, many astronomers spent much of the 1900s searching for an extra planet, dubbed Planet X, beyond the orbit of Neptune, because they believed there were anomalies in the orbits of Neptune and the other gas giants. "But it turned out that anomaly in Neptune's orbit was the result of bad observation," Levison said. The search for Planet X was called off (though some conspiracy theorists believe this was a cover up of the planet Nibiru, which they say is on a collision course for Earth.)

"You can go back 100 years to claims of planets in the outer solar system and they've all eventually gone away," he continued. "That should give you pause for thought. Just because there's not a good explanation for [the orbits of the scattered disc objects] besides another planet, doesn't mean there won't be a good explanation in future."

Brown, who discovered Sedna, said another plausible explanation for that dwarf planet's strange behavior could be that a star swung near it early in the history of our solar system, throwing it for a loop. "Back at the time of the birth of the sun, the sun probably formed in a cluster of other stars. If true, they would have been close enough together to influence each other's outer planet systems, like where Sedna is," he said.

More work is needed to determine whether Sedna and the other scattered disc objects were sent on their circuitous trips round the sun by a star that passed by long ago, or by an unseen planet that exists in the solar system right now. Finding and observing the orbits of other distant objects similar to Sedna will add more data points to astronomers' computer models. "We, and a couple of other groups of astronomers, are working hard to see if we can track some down and figure out this mystery," Brown said.

As for the putative planet itself, Levison said, "The strength of the idea that there is a planet out there will be the inability to find another explanation for these objects. But seeing it is the only way to prove it."

Copyright 2012 Lifes Little Mysteries, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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Artists' Conceptions Of Extrasolar Planets

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In this handout illustration made available on December 5, 2011 by NASA, the Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star is digitally illustrated. For the first time NASA's Kepler mission has confirmed a planet to orbit in a star's habitable zone; the region around a star, where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth, making it the smallest yet found to orbit in the middle of the habit. Clouds could exist in this earth's atmosphere, as the artist's interpretive illustration depicts. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)

In this handout illustration made available on December 5, 2011 by NASA, a diagram compares our own solar system to Kepler-22, a star system containing the first 'habitable zone' planet discovered by NASA's Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth. The diagram displays an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star and is about 2.4 times the size of Earth. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)

Artist's conception released by NASA of extrasolar planet HD 209458 b, also known as Osiris, orbiting its star in the constellation Pegasus, some 150 light years from Earth's solar system. Scientists have used an infrared spectrum -- the first ever obtained for an extrasolar planet -- to analyze Osiris' atmosphere, which is said to contain dust but no water. The planet's surface temperature is more than 700 Celsius (1330 Fahrenheit).'

Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a Jupiter-sized planet passing in front of its parent star. Such events are called transits. When the planet transits the star, the star's apparent brightness drops by a few percent for a short period. Through this technique, astronomers can use the Hubble Space Telescope to search for planets across the galaxy by measuring periodic changes in a star's luminosity. The first class of exoplanets found by this technique are the so-called 'hot Jupiters,' which are so close to their stars they complete an orbit within days, or even hours. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM

Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a unique type of exoplanet discovered with the Hubble Space Telescope. This image presents a purely speculative view of what such a 'hot Jupiter' (word dedicated to planets so close to their stars with such short orbital periods) might look like. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM

Scientist have found a new potentially habitable planet.

From the Spitzer Science Center. While astronomers have identified over 500 planets around other stars, they're all too small and distant to fill even a single pixel in our most powerful telescopes. That's why science must rely on art to help us imagine these strange new worlds. From Spitzer Space Telescope. Even without pictures of these exoplanets, astronomers have learned many things that can be illustrated in artwork. For instance, measurements of the temperatures of many "Hot Jupiters," massive worlds orbiting very close to their stars, hint that their atmospheres may be as dark as soot, glowing only from their own heat. While "Hot Jupiters" would be relatively dark in visible light, compared to their stars, their brightness is proportionally much greater in the infrared. Illustrating this dramatic contrast change helps explain why the infrared eye of NASA's Spitzer Space Telescope plays a key role in studying exoplanets. As our understanding evolves, so must the artwork. Astronomers found a blazing hot spot on the exoplanet Upsilon Andromedae b that at first, appeared to face towards its star. More data has revealed that the hottest area is actually strangely rotated almost 90 degrees away, near the day/night terminator. WASP 12b is as hot as the filament in a light bulb, and would be blazing bright to our eyes. Most interestingly, if it proves to have a strongly elliptical orbit, as first thought, calculations show it would be shedding some of its outer atmosphere ...